The present invention relates to an image-taking apparatus, and more particularly to an image-taking apparatus that enables a user to arbitrarily switch a viewfinder mode by operating a mirror unit.
A single lens reflex camera as one image-taking apparatus reflects the light emitted from an image-taking lens via a mirror closer to an image surface than the image-taking lens, and introduces the light to the optical viewfinder (“OVF”). Thereby, a photographer can view an erect object image formed by the image-taking lens. The mirror is obliquely provided on a shooting optical path.
In shooting an object image, the mirror retreats from the shooting optical path, and enables the light from the image-taking lens to such an imaging medium as a film and an image-pickup device, such as a CCD. After the shot, the mirror is obliquely arranged on the shooting optical path.
Some digital single lens reflex cameras can select two types of focusing, i.e., a manual phase difference detection and a contrast detection (Japanese Patent Application, Publication No. 2001-275033). The phase difference detection determines focus when the mirror is obliquely provided on the shooting optical path, and the contrast detection determines focus using an output from the image-pickup device, when the mirror retreats from the shooting optical path (Japanese Patent Application, Publication No. 2001-125173). A camera of Japanese Patent Application, Publication No. 2001-125173 electronically displays an image read from the image-pickup device on an electronic viewfinder (“EVF”), determines focus by the contrast detection, and measures the subject brightness using an output from the image-pickup device.
In general, the contrast detection seeks a position having a maximum AF evaluation value by slightly moving the image-taking lens in the optical axis direction, and disadvantageously requiring a long time to determine focus. On the other hand, the phase difference detection moves the image-taking lens by a detected defocus amount, and needs a shorter time to determine focus than the contrast detection.
Some digital single lens reflex cameras include a focus detecting unit of the phase difference detection in each of a lens unit and a camera body (Japanese Patent Application, Publication No. 2000-162494). According to this camera, when a mirror used to switch an optical path is located on the shooting optical path, the focus detecting unit in the camera body detects focus, and when the mirror retreats from the shooting optical path, the focus detecting unit in the lens unit detects focus. Wherever the mirror moves, the focus detecting unit detects focus by the phase difference detection and accelerates focusing.
A camera that has the mode selector that selects a shooting mode activates an EVF, when a mode selector selects a macro mode, and captures a subject image while enabling the subject image to be observed on the EVF. The camera deactivates the EVF in a shooting mode other than the macro mode, and captures a subject image while enabling the subject image to be observed on an OVF (Japanese Patent Application, Publication No. 10-336495).
Disadvantageously, the camera proposed in Japanese Patent Application, Publication No. 2000-162494 has the reduced imaging light intensity for the camera body due to the mirror that introduces the light into the focus detecting unit in the lens unit. In addition, since each of the lens unit and the camera body has the focus detecting unit, the lens unit becomes large and expensive.
The instant inventor has proposed a single lens reflex camera that displaces a mirror unit on a shooting optical path and enables a user to arbitrarily switch between the OVF mode used to introduce the light from the image-taking lens to the viewfinder optical system and focus detecting unit, and the EVF mode used to introduce the light into the image-pickup device and the focus detecting unit (see the following embodiment in this specification). This camera, whichever viewfinder mode it has, detects focus by the focus detecting unit provided in the camera body and control focus based on a detection result. This camera retreats the mirror unit from the shooting optical path during the shooting time or image recording time.
In this camera, the EVF mode in which the light reaches the image-pickup device after transmitting through the mirror unit, offsets a focus position of the subject image from a shooting time when the light reaches the image-pickup device without intervening the mirror unit, by a change of the optical path length due to a refraction in the mirror unit. Therefore, the EVF mode corrects a driving position of the focus lens, which is calculated based on the detection result by the focus detecting unit, by the offset amount of the focus position. Thus, even for the same subject distance, the target driving position of the focus lens is different between focusing in the OFV mode and focusing in the EFV mode.
As a consequence, when the user switches a current viewfinder mode among the EVF and OFV modes to the other mode while the focus lens is being driven to the target position, a defocus occurs when the driving of the focus lens ends due to the above difference between the target driving positions.
An application of a structure proposed in Japanese Patent Application, Publication No. 10-336495 to a single lens reflex camera causes a switch of viewfinder mode between the EVF and OVF modes when a shooting mode selector is operated in a playback mode use to play and display a recorded image. When the shooting mode is switched to the playback mode and the playback mode is switched back to the shooting mode, a photographer feels discomfort because a viewfinder mode for the current shooting mode is different from the viewfinder mode for the previous shooting mode.